Just as easily as you gained an alliance, you can lose one as well: when Checking Alliances if another player has more of an ally’s Power Tokens than you in their Ally Pool, or possibly by them controlling the Iron Throne (see Sitting on the Iron Throne), than that player steals the alliance from you. Follow these 3 steps:

1. That player immediately takes the house’s Shield and control of all the non-player house’s units on the Map, including its Hero and Hero Card if on the Map.

2. For each domain that you share with your former ally’s units, your units must retreat (see Retreating).

3. Since that player is gaining an alliance, they then immediately also gain any Castles that the non-player house controlled (any domain with those non-player units and a Castle).

Alliances cannot be lost during the round, unless due to an event. If you lose an Ally Token from your Ally Pool, and that brings you below 2 tokens for that ally, retain that alliance until alliances are checked at the end of the round. If no players are eligible for that alliance, then return the Shield and Hero Card (if taken) to its House Mat. The player still must retreat from all shared domains, and return any lost Castles back to their spots on the Map.